Bearing for pivotally mounted guide vanes in thermal turbomachines

ABSTRACT

A slidable bearing for pivotally mounted guide vanes in thermal turbomachines including a guide vane stem functioning as a positioning shaft and being carried in sliding bushes in the bearing support. The surface of the guide vane stem is faced with a chromium carbide layer while the bushes are preferably formed of a ceramic oxide such as aluminum oxide. With operations under severe thermal shock loads, the bushes may optionally be fabricated from silicon nitride.

United States Patent 2 1191 Prostler et a].

[75] Inventors: Wolfgang Prostler; Peter Ferschin;

Karl Lechner, all of Munchen, Germany Motoren-und Turbinen-Union MunichGmbH, Munich, Germany [22] Filed: Dec. 29, 1971 [21] Appl. No.: 213,624

[73] Assignee:

[30] Foreign Application Priority Data 2,602,714 7/1952 Wheildon, Jr.308/8 2,980,475 4/1961 Wolfe 3,022,685 2/1962 Armacost 308/8 PrimaryExaminerCharles J l Myhre Assistant Examiner-F rank Suslco Attorney-PaulM. Craig, Jr. et a1.

[57] ABSTRACT A slidable bearing for pivotally mounted guide vanes inthermal turbomachines including a guide vane stem Dec. 29, 1970 GermanyP 20 64 318.9 functioning as a positioning shaft and being carried insliding bushes in the bearing support. The surface of [52] US. Cl.308/237 the guide vane stem is faced with achromium carbide [51] Int.Cl. F 16c 33/24 layer while the bushes are preferably formed of a ee-[58] Field of Search 308/8, 241, 237 ramic oxide such as aluminum oxide.With operations under severe thermal shock loads, the bushes may op-[56] References Cited tionally be fabricated from silicon nitride.

UNITED STATES PATENTS 2,253,969 8/1941 Dawihl 308/8 13 Claims, 2 DrawingFigures v 1 L 6i 1 l 1 BEARING FOR PIVOTALLY MOUNTED GUIDE VANES INTHERMAL TURBOMACHINES BACKGROUND OF THE INVENTION The present inventionrelates to a non-lubricated bearing operative over large temperatureranges especially at high temperatures under severe stresses. Moreparticularly, the invention is concerned with a slidable bearing forpivotally mounted guide vanes in thermal turbomachines, wherein a guidevane stem serves the function of a positioning shaft and is carriedinslidable bushes in a bearing support.

Difficulty is sometimes encountered in bearings for pivotally mountedguide vanes'at the .extremely high service temperatures (about I000Cinthermal turbo- SUMMARY OF THE INVENTION The present inventionovercomes the disadvantages of the prior art by providing a slidablebearing for pivotally mounted members, preferably pivotally mountedguide vanes in thermal turbomachines, comprising a bearing support, atleast one'slidable bush seated in said bearing support constructed ofsilicon nitride or a ceramic oxide, preferably aluminum oxide, and ashaft carried in said at least one slidable bush, said shaft being facedwith a chromium carbide layer. Most advantageously, the chromium carbidelayer is deposited on the shaft by flame or plasma spraying.

, The invention is further directed to a slidable bearing for pivotallymounted members, such as pivotally mounted guide vanes in thermalturbomachines, comprising a bearing support, at least one outer bush ofa ceramic oxide, preferably aluminum oxide, seated in said bearingsupport, a shaft (guide vane stem serving as a position shaft), and atleast one inner bush of a ceramic oxide, preferably aluminum oxide,bonded to said shaft by a highly temperature resistant adhesive andarranged to engage said at least one outer bush.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE INVENTIONWith reference to FIG. I, a guide vane I carried on a vane stem or shaft2 is, pivotally mounted in a bearing support 3. The vane stem 2, whichserves as a positioning shaft, is faced with a chromiumcarbide layer 4.Force fitted into the stepped inner and outer seats of the bearingsupport 3 are, respectively, a slidable bush 6i and a slidable bush 6a.The vane stem is pivotally mounted in the slidable bushes 6i and, 6awhich are preferably made of aluminum oxide (A1 0 The bearing serves theconcomitant functions of radial and axial support in that a stop collar7 intervening between the stem 2 and the vane l bears against the faceof slidable bush 6i. A positioning lever 9 is frictionally held againstthe stem 2 with screws 10 and secures a washer 8 against the face of theouter slidable bush 6a.

' It has been demonstrated that, when the guide vane stem is faced withchromium carbide- (CrC and the bushes are constructed of a ceramicoxide, preferably aluminum oxide (A1 0 the guide vane stem of thepresent invention, taken in conjunction with a steel bearing support,will be adequately adjustable with a minimum amount of clearance attemperatures of about 1000C, at which temperature the steel bearingsupport is heated to a red glow, without any need for cooling orlubrication. At these temperatures, the torque expended at the shaft topivot it is practically the same as in a cold condition. Further, thisbearing assembly operates substantially in the absence of any wear. I

The chromium carbide layer is most advantageously deposited on the vanestem by flame or plasma sprayin'g employing conventional methods. Thisoffers a maximum bond of the coatingwith the stem and produces astructure ideally suited for slidable bearings.

Aluminum oxide is preferred as the ceramic oxide material of thebushings by virtue of its ability to withstand great abuse or stresses.However, where severe thermal shock loads are anticipated, the bushesmay be comprised of silicon nitride (Si N instead.

With reference to FIG. 2, bonded by means of a highly temperatureresistant adhesive 12 (preferably of thetwo component type) to a guidevane stem 2 of a guide vane 1 are two preferably aluminum oxide busheslli and 11a. The vane stem 2 is carried through bushes lli and 11a inpreferably aluminum oxide bushes 6i and 6a which are force fitted intostepped seats in a bore 5 in a bearing support 3. This hearing likewiseserves for simultaneously radial and axial support,

using washers 7, 8 and a positioning lever 9 much as in FIG.'l.

Vane stem 2 of this embodiment, like FIG. 1, may be coated with chromiumcarbide. Also, one or both sets of bushes 6i, 6a and lli, 11a may beoptionally jacketed or made from silicon nitride where severe thermalshock loads are anticipated.

It is understood that the embodiments disclosed herein are susceptibleto numerous changes and modifications, as will be apparent to a personskilled in the art. Accordingly, the present invention is not limited tothe details shown and described herein but intended to cover any suchchanges and modifications within the scope of the invention.

We claim: 1

1. A slidable bearing for pivotally mounted members comprising a bearingsupport, at least one slidable bush seated in said bearing support, saidat least one slidable bush being made of a material selected from thegroup consisting of a ceramic oxide and silicon nitride, and a shaftcarried in said at least one slidable bush, said shaft having a chromiumcarbide coating thereon.

2. A slidable bearing according to claim 1, wherein said at least oneslidable bush is constructed of aluminum oxide.

3. A slidable bearing according to claim 1, wherein said chromiumcarbide coating is deposited on said shaft by flame or plasma spraying.

4. A slidable bearing according to claim 1, wherein said at least oneslidable bush is constructed of silicon nitride.

5. A slidable bearing for pivotally mounted guide vanes in thermalturbomachines comprising a bearing support, slidable bushes seated insaid bearing support, said slidable bushes being constructed of one of aceramic oxide and silicon nitride, and a guide vane stem functioning asa positioning shaft carried in said slidable bushes, said stem beingfaced with a chromium carbide layer.

6. A slidable bearing according to claim 5, wherein said bushes areconstructed of aluminum oxide.

7. A slidable bearing according to claim 1, wherein said bushes areconstructed of silicon nitride.

8. A slidable bearing according to claim 1, wherein one end of saidshaft is connected to a guide vane of a thermal turbomachine.

9. A slidable bearing according to claim 8, wherein the end of saidshaft opposite said one end is connected to a positioning lever suchthat movement of said positioning lever effects pivotal movement of saidshaft and said guide vane.

10. A slidable bearing according to claim 5, wherein one end of saidstem is connected to a guide vane of a thermal turbomachine.

11. A slidable bearing according to claim 10, wherein the end of saidstern opposite said one end is connected to a positioning lever suchthat movement of said positioning lever effects pivotal movement of saidstem and said guide vane.

12. A slidable bearing according to claim 9, further comprising a washeradjacent said positioning lever and a stop collar at said guide vane,wherein said at least one slidable bush includes a first slidable bushdisposed with an end face against said washer and a second slidable bushwith an end face against said stop collar.

13. A slidable bearing according to claim 11, further comprising awasher adjacent said positioning lever and a stop collar at said guidevane, wherein said at least one slidable bush includes a first slidablebush disposed with an end face against said washer and a second slidablebush with an end face against said stop collar.

2. A slidable bearing according to claim 1, wherein said at least oneslidable bush is constructed of aluminum oxide.
 3. A slidable bearingaccording to claim 1, wherein said chromium carbide coating is depositedon said shaft By flame or plasma spraying.
 4. A slidable bearingaccording to claim 1, wherein said at least one slidable bush isconstructed of silicon nitride.
 5. A slidable bearing for pivotallymounted guide vanes in thermal turbomachines comprising a bearingsupport, slidable bushes seated in said bearing support, said slidablebushes being constructed of one of a ceramic oxide and silicon nitride,and a guide vane stem functioning as a positioning shaft carried in saidslidable bushes, said stem being faced with a chromium carbide layer. 6.A slidable bearing according to claim 5, wherein said bushes areconstructed of aluminum oxide.
 7. A slidable bearing according to claim1, wherein said bushes are constructed of silicon nitride.
 8. A slidablebearing according to claim 1, wherein one end of said shaft is connectedto a guide vane of a thermal turbomachine.
 9. A slidable bearingaccording to claim 8, wherein the end of said shaft opposite said oneend is connected to a positioning lever such that movement of saidpositioning lever effects pivotal movement of said shaft and said guidevane.
 10. A slidable bearing according to claim 5, wherein one end ofsaid stem is connected to a guide vane of a thermal turbomachine.
 11. Aslidable bearing according to claim 10, wherein the end of said stemopposite said one end is connected to a positioning lever such thatmovement of said positioning lever effects pivotal movement of said stemand said guide vane.
 12. A slidable bearing according to claim 9,further comprising a washer adjacent said positioning lever and a stopcollar at said guide vane, wherein said at least one slidable bushincludes a first slidable bush disposed with an end face against saidwasher and a second slidable bush with an end face against said stopcollar.
 13. A slidable bearing according to claim 11, further comprisinga washer adjacent said positioning lever and a stop collar at said guidevane, wherein said at least one slidable bush includes a first slidablebush disposed with an end face against said washer and a second slidablebush with an end face against said stop collar.